1. Field of the Invention
The present invention relates to a power semiconductor device, and more particularly, to a power semiconductor device capable of improving voltage spike effect produced during switching and stability of the manufacturing process.
2. Description of the Prior Art
A trench power transistor is a typical semiconductor device in power management application, such as switching power supplies, power control ICs of computer systems or peripherals, power supplies of backlight, motor controllers, etc. With the high switching speed of the trench power transistor, a voltage spike effect produced during switching may affect operating performance. Therefore, to solve the above-mentioned problem, the ratio of the input capacitance to the reverse transfer capacitance of the trench power transistor needs to be enhanced to an optimal value for suppressing the voltage spike effect.
In order to improve the voltage spike effect produced during switching, the prior art provides modifications on the structure of the trench power transistor to optimize the ratio of the input capacitance to the reverse transfer capacitance. For example, U.S. Pat. No. 7,253,473, U.S. Pat. No. 7,037,788, U.S. Pat. No. 6,809,349, U.S. Pat. No. 6,806,548, and U.S. Pat. No. 6,777,295 disclose trench semiconductor devices which form a gate electrode upon the trench surface by reducing the trench depth, so as to enhance the ratio of the input capacitance to the reverse transfer capacitance of the trench power transistor. However, through the above-mentioned structures, several problems, such as non-uniform implant or unusual P-N junction avalanche, often occur.